In B707 days even abnormal procedures were done by memory. Manufacturers changed to check lists for a good reason. Doing things by memory opens a possibility of forgetting or committing an error. Pilots in airline come from different backgrounds and environments or have switched to different make. Sometimes an airline has different variants of the same aircraft in which things are done differently. So use of check list is an accepted practice. The manufacturer builds an aircraft on a design philosophy and it's safer to follow their procedures. Due to some specific regional or operational pecularity sometimes a few things may have to be done differently but even those changes should be incorporated after consultation with the manufacturer.